CN112129483B - Ablation ground simulation test device and method based on ablation backset compensation - Google Patents
Ablation ground simulation test device and method based on ablation backset compensation Download PDFInfo
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- G01M—TESTING STATIC OR DYNAMIC BALANCE OF MACHINES OR STRUCTURES; TESTING OF STRUCTURES OR APPARATUS, NOT OTHERWISE PROVIDED FOR
- G01M9/00—Aerodynamic testing; Arrangements in or on wind tunnels
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- B64—AIRCRAFT; AVIATION; COSMONAUTICS
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- G01M—TESTING STATIC OR DYNAMIC BALANCE OF MACHINES OR STRUCTURES; TESTING OF STRUCTURES OR APPARATUS, NOT OTHERWISE PROVIDED FOR
- G01M9/00—Aerodynamic testing; Arrangements in or on wind tunnels
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- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
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Abstract
The invention relates to an ablation ground simulation test device and method based on ablation backset compensation, and belongs to the technical field of aerospace aircrafts. The method comprises the steps of acquiring a thermal response video of a tested model in the test process, capturing a surface boundary of the model by using an image processing technology, acquiring surface boundary movement change dynamic information, identifying to obtain the surface ablation retreating rate of the tested model, feeding back the surface retreating rate or retreating amount to a servo control system, compensating position deviation caused by the retreating of the surface of the tested model through a servo motor and a transmission system, and ensuring the stability of the environmental state of the tested model in the test process.
Description
Technical Field
The invention relates to an ablation ground simulation test device and method based on ablation backset compensation, in particular to an ablation ground simulation test device and method of a heat-proof material or a heat protection system, and belongs to the technical field of aerospace aircrafts.
Background
Before actual flight, a high-speed aircraft thermal protection material or a thermal protection system usually needs to perform an ablation ground simulation test for detecting whether the surface (outer mold line) receding amount and the temperature response condition of the thermal protection material in a high-temperature environment meet the design requirements. The ground test equipment for simulating the thermal protection material or the thermal protection system of the aircraft generally comprises an electric arc wind tunnel, a plasma wind tunnel, a gas flow wind tunnel, oxyacetylene flame, oxypropylene flame, quartz lamp or carbon lamp radiation heating and the like. The existing ablation ground simulation test is carried out by adopting a traditional passive feedback-free ablation ground simulation test system, and the specific test method comprises the following steps: before the test is carried out, a model provided with a heat flux density or temperature sensor is firstly placed at a position away from the outlet of a high-temperature fluid spray pipe or a heat source of a high-temperature heating body by a certain distance, and the response conditions of various sensors are monitored by adjusting the power of the heat source, a working medium or the position of the model until the heat flux density or the surface temperature measured by the sensors is inhibited from design and evaluation environmental parameters. And then recording design operation parameter information of a working medium, a power supply system, a model workbench position, other auxiliary systems and the like as fixed test parameters of a thermal protection material or a thermal protection system simulation test in a design environment.
However, the existing passive ablation ground simulation test system without feedback has the following disadvantages:
(1) The position of a test model in a traditional ablation ground simulation test system of a heat-proof material or a heat protection system is fixed, the material surface is usually ablated due to high temperature in the test process to generate boundary retreat, so that the actual surface position of the model deviates from the nominal position when the test state is determined, the actual bearing environment state of the test model deviates from the set state, and the state deviation degree is increased along with the increase of ablation retreat amount.
(2) The ablation backing amount is usually determined by measuring the height difference of a model at specified positions before and after a test in a traditional ablation ground simulation test system for the heat-proof material or the heat protection system, and the backing quantitative value of the model surface in the test process cannot be usually obtained, namely the real-time ablation backing rate of the measured model surface cannot be obtained.
Disclosure of Invention
The technical problem solved by the invention is as follows: the ablation ground simulation test device and the ablation ground simulation test method based on ablation retreat amount compensation are used for overcoming the defects of the prior art, the ablation retreat rate of a tested model is obtained in real time in the test process, the deviation between the ablation surface of the tested model, which is caused by the retreat of the surface of the tested model, relative to the ablation test reference position is compensated, and the stability of the environmental state of the tested model in the test process is ensured.
The technical scheme of the invention is as follows: an ablation ground simulation test device based on ablation retreat amount compensation comprises an image collector, an image processing computer, a servo controller, a first servo motor, a movable workbench and a movable workbench movement track;
the movable workbench is arranged on the moving track of the movable workbench and is used for bearing the tested model;
the image collector is used for recording the test process of the tested model to obtain continuous video information and transmitting the video information to the image processing computer;
the image processing computer is used for resolving the video information into single frame RGB images at different moments, analyzing to obtain boundary information of a tested model in each single frame RGB image, obtaining a surface ablation rate of the tested model associated with time based on pixels and a physical length comparison table calibrated by a standard reference object according to the boundary information of the tested model in the single frame RGB images at different moments, and sending the surface ablation rate of the tested model in the latest calculated period to a servo controller according to a preset sampling period to calculate the surface ablation backward quantity of the tested model in the current sampling period;
the servo controller judges whether the ablation backward quantity of the surface of the tested model is larger than a preset boundary movement adjusting threshold value or not, if so, a motor control signal in a PWM form is generated, otherwise, a motor control signal in a fixed level form is generated, and the motor control signal is sent to the first servo motor;
the first servo motor drives the movable workbench to move along the moving track of the movable workbench under the action of a motor control signal, and compensates the ablation retreat quantity of the tested model, so that the tested model is kept at the ablation test reference position and is unchanged; the image collector is synchronously driven to move along the direction parallel to the moving track of the moving workbench, so that the relative position of the image collector and the ablation test reference position is kept unchanged.
The movable workbench and the movable workbench movement track are positioned in the wind tunnel for the ablation ground simulation test; the image collector, the image processing computer, the servo controller and the servo motor are positioned outside the wind tunnel for the ablation ground simulation test; the wind tunnel for the ablation ground simulation test is provided with a transparent observation window, the image collector records a video of the test process of the tested model through the observation window, and the optical axis of the image collector is parallel to the ablation surface of the tested model and is vertical to the axis of the moving track of the movable workbench.
According to the image collector, the filtering lens is adopted outside the lens to protect the CCD of the image collector from overexposure, and the water circulation cooling system is adopted around the lens to protect the CCD of the image collector, so that the temperature of the outer surface of the image collector is not higher than 45 ℃.
The moving track of the moving workbench is made of nickel-based superalloy, the surface of the moving track is sprayed with yttrium-stabilized zirconia coating material, and the highest surface of the moving track can tolerate the temperature of 1000 ℃.
The movable working tables are protected by a high-pressure water circulating cooling system, and the temperature of the device exposed to the action of high-temperature gas is not higher than 150 ℃.
The ablation ground simulation test device based on the ablation backward quantity acquisition and compensation further comprises a second servo motor, wherein the second servo motor is arranged in the wind tunnel for the ablation ground simulation test;
the servo controller is used for synchronously sending the motor control signal to the servo motor and the second servo motor;
the servo motor is used for driving the transmission device and the movable workbench to move along the moving track of the movable workbench and compensating ablation retreating displacement of the tested model so that the tested model keeps an ablation test reference position unchanged;
and the second servo motor is used for driving the image collector, and the first servo motor and the second servo motor work synchronously to ensure that the relative position of the image collector and the ablation test reference position is kept unchanged.
The specific steps of the image processing computer for acquiring the boundary information of the tested model in the single frame RGB image are as follows:
(a) Converting the RGB test image into a gray-scale image;
(b) Filtering all pixel point gray levels to pixel points smaller than a preset gray threshold value, and setting all pixel point gray levels larger than the preset gray threshold value as designated numerical values to obtain a boundary area picture;
(c) Scanning the boundary region picture line by line, scanning all pixel points in each line one by one, continuously taking three pixel points, and marking as a first pixel point, a second pixel point and a third pixel point, if the gray value X1 of the first pixel point, the gray value X2 of the second pixel point and the gray value X3 of the third pixel point simultaneously meet the following two conditions, determining that the second pixel point or the third pixel point is the pixel point of the boundary of the measured model in the boundary region picture, and if not, determining that the first pixel point, the second pixel point and the third pixel point are not the pixel points of the boundary of the measured model in the boundary region picture;
the first condition is as follows:
the ratio of the absolute value of the difference between X1 and X2 to the average of X1 and X2 is less than 10%, i.e. 2 gaming defects X1-X2 |/(X1 + X2) <10%;
the second condition is as follows:
the ratio of the absolute value of the difference between X1 and X3 to the average value of X1 and X3 is greater than 50%, i.e., 2 calvities X1-X3 |/(X1 + X3) >50%.
The ablation rate of the surface of the tested model related to time
The calculation formula of (c) is as follows:
wherein, Δ P = [ Δ P = 1 ,ΔP 2 ,...,ΔP n ]For the difference of the position of each pixel point of the boundary of the tested model, delta P i I = n is the position difference of the ith pixel point of the boundary in the tested model checking image, n is the number of the boundary pixel points in the tested model checking image, and L is the corresponding physical size of the single pixel point in the tested model checking image.
The calculation formula of the surface ablation quantity R of the tested model related to the time is as follows:
wherein S is the sampling period.
The threshold value is not lower than the minimum displacement of the servo motor capable of controlling the moving track of the moving workbench, and the set range is 0.05-1.00 mm.
The invention provides another technical solution that: an ablation ground simulation test method based on ablation backset amount acquisition and compensation comprises the following steps:
s1, mounting a tested model on a movable workbench, mounting the movable workbench on a moving track of the movable workbench, and adjusting the position and the angle of an image collector to enable the optical axis of the image collector to be parallel to the ablation surface of the tested model and to be perpendicular to the axis of the moving track of the movable workbench;
s2, starting a wind tunnel for an ablation ground simulation test, starting the ablation ground test, simultaneously recording a video of the test process of the tested model by adopting an image collector to obtain continuous video information, and transmitting the video information to an image processing computer;
s3, the image processing computer resolves the video information into single-frame RGB images at different moments, analyzes the single-frame RGB images to obtain boundary information of the tested model in each single-frame RGB image, and obtains the surface ablation rate of the tested model associated with time based on a pixel and physical length comparison table calibrated by a standard reference object according to the boundary information of the tested model in the single-frame RGB images at different moments;
s3, the image processing computer calculates the ablation rate of the surface of the tested model which is obtained by the latest calculation according to a preset sampling period, calculates the ablation back quantity of the surface of the tested model which is obtained by the current sampling period and sends the calculated ablation back quantity to the servo controller, and the step S4 is carried out;
s4, the servo controller judges whether the ablation backward quantity of the surface of the tested model is larger than a preset boundary movement adjusting threshold value or not, if so, the step S5 is executed, and if not, the step S6 is executed;
s5, the servo controller drives the movable workbench to move along the moving track of the movable workbench, and the ablation recession of the tested model is compensated;
s6, judging whether the current analysis time reaches the preset test time or not by the image processing computer, and ending the test if the current analysis time reaches the preset test time; and if the test time is not reached, skipping to the step S3 to repeatedly execute the step S3 to the step S6.
Compared with the prior art, the invention has the beneficial effects that:
(1) The real-time acquisition method of ablation retreat rate and ablation retreat quantity in the ablation ground simulation test of the heat-proof material or the heat protection system is adopted, so that the timely acquisition of the ablation retreat rate of the surface of the tested model in the ablation test is realized, and compared with the method for calculating the total ablation retreat quantity of the material thickness before and after the measurement test in the prior art, richer scientific experimental data are acquired.
(2) The invention adopts the image processing computer, the servo controller and the servo motor system combined system, realizes the real-time compensation of the boundary position change of the measured model, and ensures the precision of the heated surface test position of the measured model in the test process.
(3) The method and the device have the advantages that accurate displacement compensation is carried out by obtaining ablation retreat information of the measured model, so that the accurate maintenance capability of the assessment environment is improved, compared with a test method in the prior art that the deviation between the nominal test state and the actual test state is larger due to the fact that the model position is not adjusted, the deviation between the nominal test state and the actual test state in the ablation ground simulation test of the heat-proof material or the heat protection system is reduced, and the environment maintenance accuracy of the ground test is guaranteed.
Drawings
FIG. 1 is a block diagram of an ablation ground simulation test device based on ablation backset compensation according to an embodiment of the invention;
in the figure: 1 is an image collector; 2, an image processing computer; 3 is a servo controller; 4 is a test model; 5-1 is a first servo motor; 5-2 is a second servo motor; 6 is a movable workbench; 7 is a moving track of the movable workbench; 8 is a wind tunnel for ablation ground simulation test;
FIG. 2 is a flowchart of a ground simulation test system for ablation back-off acquisition and compensation according to an embodiment of the present invention;
fig. 3 is an RGB image acquired by the image acquisition device at the initial time t =0.00s according to the embodiment of the present invention;
fig. 4 is a gray scale image obtained by processing an initial time t =0.00sRGB image according to the embodiment of the present invention;
fig. 5 is a high temperature area on the surface of the test model obtained by identifying the image of the area with the initial time t =0.00s according to the embodiment of the invention;
fig. 6 is a surface boundary identified at an initial time t =0.00s according to an embodiment of the present invention;
FIG. 7 illustrates an embodiment of the present invention comparing an initial time t =0.00s recognition boundary with an RGB image;
fig. 8 shows the surface boundary identified by t =0.20s according to the embodiment of the present invention;
fig. 9 is a comparison of the surface boundaries identified in fig. 9 t =0.00s and t =0.20s according to the embodiment of the present invention;
FIG. 10 is a plot of experimental model ablation rates calculated over time for an embodiment of the present invention;
FIG. 11 is a calculated trial model ablation setback along a time history for an embodiment of the present invention;
FIG. 12 is a graph of a control signal for displacement along the time history as provided by the experimental procedure of an embodiment of the present invention.
Detailed Description
The invention is further illustrated by the following examples.
Example 1:
the invention provides an ablation ground simulation test device based on ablation backset compensation, which comprises an image collector 1, an image processing computer 2, a servo controller 3, a first servo motor 5-1, a movable workbench 6 and a movable workbench moving track 7, wherein the image collector comprises a first servo motor and a second servo motor;
the movable workbench 6 is arranged on the movable workbench moving track 7 and is used for bearing the tested model 4;
the image collector 1 is used for recording the test process of the tested model 4 to obtain continuous video information and transmitting the video information to the image processing computer 2;
the image processing computer 2 is used for resolving the video information into single frame RGB images at different moments, analyzing and obtaining boundary information of the tested model in each single frame RGB image, obtaining the surface ablation rate of the tested model associated with time based on the pixel calibrated by the standard reference object and a physical length comparison table according to the boundary information of the tested model in the single frame RGB images at different moments, and sending the surface ablation backing quantity of the tested model in the current sampling period obtained by calculating according to a preset sampling period to the servo controller 3;
the servo controller 3 judges whether the ablation backward quantity of the surface of the tested model is larger than a preset boundary movement adjusting threshold value or not, if so, a motor control signal in a PWM form is generated, otherwise, a motor control signal in a fixed level form is generated, and the motor control signal is sent to the first servo motor 5-1; preferably, the threshold is not lower than the minimum displacement of the servo motor capable of controlling the moving track 7 of the moving workbench, and the set range is 0.05-1.00 mm.
The first servo motor 5-1 drives the movable workbench 6 to move along the movable workbench moving track 7 under the action of a motor control signal, and compensates ablation backward quantity of the tested model, so that the tested model is kept at an ablation test reference position and is not changed; and synchronously driving the image collector 1 to move along the direction parallel to the moving track 7 of the moving workbench, so that the relative position of the image collector and the ablation test reference position is kept unchanged. The specific method for compensating the ablation recession of the tested model can select the average recession of two or more points of one point to compensate.
The movable workbench 6 and the movable workbench moving track 7 are positioned in a wind tunnel 8 for the ablation ground simulation test, and the wind tunnel 8 for the ablation ground simulation test is a closed structure containing high-temperature gas. The image collector 1, the image processing computer 2, the servo controller 3 and the servo motor 5 are positioned outside the wind tunnel 8 for the ablation ground simulation test; a transparent observation window is arranged on the wind tunnel for the ablation ground simulation test, the image collector 1 records a video of the test process of the tested model through the observation window, and the optical axis of the image collector 1 is parallel to the ablation surface of the tested model 4 and is vertical to the axis of the moving track 7 of the moving workbench. After the wind tunnel 8 for the ablation ground simulation test is started, the image collector 1 collects the test of the test model 4 for video recording, and the video recording is transmitted to the image processing computer 2 for image processing.
Preferably, the image collector 1 adopts a filter lens to protect the lens so as to ensure that the CCD of the image collector 1 is not overexposed, and adopts a water circulation cooling system to protect the periphery so as to ensure that the temperature of the outer surface of the image collector 1 is not higher than 45 ℃.
Preferably, the moving track 7 of the moving workbench is made of nickel-based superalloy, the surface of which is sprayed with yttrium-stabilized zirconia coating material, and the highest surface of the track can withstand the temperature of 1000 ℃.
Preferably, the movable working table 6 is protected by a high-pressure water circulating cooling system, and the temperature of the device exposed to the high-temperature gas is not higher than 150 ℃.
Preferably, the specific steps of the image processing computer 2 acquiring the boundary information of the tested model in the single frame RGB image are as follows:
(a) Converting the RGB test image into a gray-scale image;
(b) Filtering all pixel point gray levels to pixel points smaller than a preset gray threshold value, and setting all pixel point gray levels larger than the preset gray threshold value as designated numerical values to obtain a boundary area picture;
(c) Scanning the boundary region picture line by line, scanning all pixel points in each line one by one, continuously taking three pixel points, and marking as a first pixel point, a second pixel point and a third pixel point, if the gray value X1 of the first pixel point, the gray value X2 of the second pixel point and the gray value X3 of the third pixel point simultaneously meet the following two conditions, determining that the second pixel point or the third pixel point is the pixel point of the boundary of the detected model in the boundary region picture, and if not, determining that the first pixel point, the second pixel point and the third pixel point are not the pixel points of the boundary of the detected model in the boundary region picture;
the first condition is as follows:
the ratio of the absolute value of the difference between X1 and X2 to the average of X1 and X2 is less than 10%, i.e. 2 gaming defects X1-X2 |/(X1 + X2) <10%;
the second condition is as follows:
the ratio of the absolute value of the difference between X1 and X3 to the average value of X1 and X3 is greater than 50%, i.e., 2% Y X1-X3 |/(X1 + X3) >50%.
The ablation rate of the surface of the tested model related to time
The calculation formula of (a) is as follows:
wherein, Δ P = [ Δ P = 1 ,ΔP 2 ,...,ΔP n ]For the difference of the position of each pixel point of the boundary of the tested model, delta P i I = n is the position difference of the ith pixel point of the boundary in the tested model checking image, n is the number of the boundary pixel points in the tested model checking image, and L is the corresponding physical size of the single pixel point in the tested model checking image.
The calculation formula of the surface ablation R of the tested model related to the time is as follows:
wherein S is the sampling period.
The wind tunnel for the ablation ground simulation test can be an electric arc wind tunnel, a plasma wind tunnel or a gas flow wind tunnel. The ablation ground simulation test comprises a plasma flame ablation test, an oxyacetylene flame ablation test, a gas flame ablation test, an oxypropylene flame ablation test, a quartz lamp ablation test, a carbon lamp radiation heating ablation test and the like.
For a wind tunnel 8 for ablation ground simulation test with no vacuum or closed environment requirement in a test section, the movable workbench 6 and the movable workbench motion track 7 can be connected in parallel for use and driven by one servo motor 5.
The image processing computer 2 and the servo controller 3 can be directly integrated in one computer in a hardware card mode, and the image processing and the control signal processing on the same platform are realized.
Based on the device, the invention also provides an ablation ground simulation test method based on ablation backset acquisition and compensation, as shown in fig. 2, the method comprises the following steps:
s1, installing a tested model 4 on a movable workbench 6, installing the movable workbench 6 on a movable workbench motion track 7, and adjusting the position and the angle of an image collector 1 to ensure that the optical axis of the image collector 1 is parallel to the ablation surface of the tested model 4 and is vertical to the axis of the movable workbench motion track 7;
s2, starting a wind tunnel 8 for an ablation ground simulation test, starting the ablation ground test, simultaneously recording a video of the test process of the tested model 4 by adopting the image collector 1 to obtain continuous video information, and transmitting the video information to the image processing computer 2;
s3, the image processing computer 2 resolves the video information into single frame RGB images at different moments, analyzes and obtains boundary information of the tested model in each single frame RGB image, and obtains the surface ablation rate of the tested model associated with time based on a pixel and physical length comparison table calibrated by a standard reference object according to the boundary information of the tested model in the single frame RGB images at different moments;
s3, the image processing computer 2 calculates the ablation rate of the surface of the tested model which is obtained by the latest calculation according to a preset sampling period, calculates the ablation back quantity of the surface of the tested model which is obtained by the current sampling period and sends the calculated ablation back quantity to the servo controller 3, and the step S4 is entered;
s4, the servo controller 3 judges whether the ablation retreat quantity of the surface of the tested model is larger than a preset boundary movement adjustment threshold value, if so, the step S5 is executed, and if not, the step S6 is executed;
s5, the servo controller 3 drives the movable workbench 6 to move along the movable workbench moving track 7, and ablation recession of the tested model is compensated;
s6, the image processing computer 2 judges whether the current analysis time reaches the preset test time, and if the current analysis time reaches the preset test time, the test is finished; and if the test time is not reached, skipping to the step S3 to repeatedly execute the step S3 to the step S6.
Example 2:
as shown in fig. 1, another ablation ground simulation test device based on ablation backset amount acquisition and compensation is provided in another embodiment of the present invention, and the device further includes a second servo motor 5-2 on the basis of embodiment 1, and the second servo motor is placed inside a wind tunnel for ablation ground simulation test;
the servo controller 3 synchronously sends the motor control signal to the servo motor 5-1 and the second servo motor 5-2;
the servo motor 5-1 is used for driving the transmission device and the movable workbench 6 to move along the movable workbench moving track 7, compensating ablation backward displacement of the tested model, and keeping the reference position of the ablation test of the tested model unchanged;
and the second servo motor 5-2 is used for driving the image collector 1, and the first servo motor 5-1 and the second servo motor 5-2 work synchronously to ensure that the relative position of the image collector and the ablation test reference position is kept unchanged.
In the embodiment, the electric arc wind tunnel ablation ground test is taken as an example, and ablation data and material ablation response difference which can be obtained before and after the implementation of the method are compared by selecting the same heat-proof material and the same ground test state.
The ground test steps and results of the original electric arc wind tunnel ablation without implementing the method are as follows:
1) Selecting an electric arc wind tunnel as an ablation material thermal protection test platform, and debugging test state parameters by a phi 80mm ball head cylinder model: air medium, 300K wall temperature heat flux density 6000kW/m 2 The air total enthalpy value is 20MJ/kg, the pressure is 3600Pa, the heating time is 30s, and the operation parameters of the test equipment and the installation and fixing positions of the models are recorded.
2) Selecting a phi 80mm x 60mm ball-head cylindrical light carbon/phenolic aldehyde heat-proof material as a test material, measuring and recording the initial thickness of the model to be l1=60.02mm, and installing the test material to a test station.
3) And presetting recorded equipment operation parameters, starting wind tunnel test equipment, and completing a 30s electric arc wind tunnel test.
4) And after the safety locking of the test equipment system is released, taking out the test model, measuring the thickness of the model after the test to be l2=49.49mm, and obtaining the ablation retreat quantity of the phi 80mm multiplied by 60mm light carbon/phenolic material under the test state to be delta l = l1-l2=8.53mm.
The arc wind tunnel ablation ground test method implemented by the invention comprises the following steps and results:
1) Selecting an electric arc wind tunnel as an ablation material thermal protection test platform, and debugging test state parameters by a phi 80mm ball head cylinder model: air medium, 300K wall temperature heat flux density 6000kW/m 2 The total enthalpy value of air is 20MJ/kg, the pressure is 3600Pa, the heating time is 200s, and the running parameters of the test equipment and the installation and fixing position of the model are recorded; according to the connection relation shown in fig. 1, the image collector 1, the image processing computer 2, the servo controller 3, the servo motor 5, the transmission device, the movable workbench 6, the movable workbench movement track 7 and the ground test system 8 are connected, and the testing and checking of each instrument and equipment ensure that the working states of all instruments are normal.
2) And starting the image collector 1 and the image processing computer 2, and completing the corresponding size calibration of the standard frame obtained by the image collector 1 by using a standard test model, wherein the calibration result of the test is that the corresponding size of 1280 multiplied by 720 pixels is 176.27 multiplied by 99.15mm.
3) Selecting a phi 80mm multiplied by 60mm ball head cylindrical lightweight carbon/phenolic aldehyde heat-proof material as a test model 4, measuring and recording the initial thickness of the model to be l1=60.12mm, and installing the test material to a test station.
4) Presetting recorded equipment operation parameters, starting wind tunnel test equipment, starting an image collector 1, an image processing computer 2, a servo controller 3 and a servo motor 5, and setting a threshold value of servo motor driving operation as that the surface back-off amount reaches 0.5mm.
5) The first frame of RGB test image is obtained as shown in fig. 3 and the image is converted to a gray scale image as shown in fig. 4. Filtering all the pixel points to the pixel points with the gray scale less than 200 and setting the gray scale value of the pixel points with the gray scale greater than 200 as 250 to obtain the boundary region picture as shown in fig. 5.
6) Scanning all pixel points line by line, continuously taking gray values X1, X2 and X3 of three pixel points, wherein the ratio of the absolute value of the gray value difference of the X1 pixel points and the X2 pixel points to the average value of the gray value difference is less than 10%, namely 2 n (X1-X2) |/(X1 + X2) <10%; and the ratio of the absolute value of the gray value difference of the X1 pixel point and the X2 pixel point to the average value of the two is more than 50%, namely 2Y X1-X2 |/(X1 + X2) >50%, and the boundary is determined. The boundary of the first frame of the measured model obtained by identification is shown in fig. 6. Comparing the RGB test image with the recognized boundary, the process can capture the boundary of the model under test well, as shown in FIG. 7.
7) Next, a second frame of image is read in, and the boundary of the obtained model to be tested is identified as shown in fig. 8. By comparing the ablation boundaries at times t =0.00s and t =0.02s, the ablation setback of the initial 0.2s is calculated, as shown in fig. 9.
8) Similarly, the model pictures captured by the image acquisition unit 1 are continuously read, the ablation backing-off rate of the model surface is obtained as shown in 10, the cumulative ablation backing-off amount along the time is obtained as shown in fig. 11, and the displacement control signal transmitted to the servo controller is shown in fig. 12.
9) According to the model boundary captured by the image collector 1, the finally obtained calculated ablation retreating amount is 9.77mm, the servo controller starts controlling for 19 times, each time, the displacement is 0.5mm, the displacement compensation amount is 9.50mm, and the control time axis is shown in figure 12.
10 After the safety locking of the test equipment system is released, the test model is taken out, the thickness of the model after the test is measured to be l2=50.29mm, and the ablation recession of the light carbon/phenolic material with the diameter of 80mm multiplied by 60mm under the test state is obtained to be delta l = l1-l2=9.83mm. The ablation retreat value is actually measured and calculated to be 0.06mm by image identification. Compared with a test state without feedback control, the ablation retreating amount is increased by 1.30mm, the ablation retreating amount reduction caused by the change of the test state is compensated, the test assessment environment maintaining precision is improved, and important accurate quantitative data reference is provided for thermal protection engineering designers.
Although the present invention has been described with reference to the preferred embodiments, it is not intended to limit the present invention, and those skilled in the art can make possible variations and modifications of the present invention using the method and the technical contents disclosed above without departing from the spirit and scope of the present invention, and therefore, any simple modifications, equivalent changes and modifications made to the above embodiments according to the technical essence of the present invention are all within the scope of the present invention.
Claims (10)
1. An ablation ground simulation test device based on ablation retreat amount compensation is characterized by comprising an image collector (1), an image processing computer (2), a servo controller (3), a first servo motor (5-1), a movable workbench (6) and a movable workbench movement track (7);
the movable workbench (6) is arranged on the movable workbench moving track (7) and is used for bearing the tested model (4);
the image collector (1) is used for recording the test process of the tested model (4) to obtain continuous video information and transmitting the video information to the image processing computer (2);
the image processing computer (2) is used for resolving the video information into single frame RGB images at different moments, analyzing to obtain boundary information of the tested model in each single frame RGB image, obtaining the surface ablation rate of the tested model associated with time based on a pixel and physical length comparison table calibrated by a standard reference object according to the boundary information of the tested model in the single frame RGB images at different moments, calculating the surface ablation rate of the tested model obtained by the latest calculation according to a preset sampling period, and sending the calculated surface ablation back quantity of the tested model in the current sampling period to the servo controller (3);
the servo controller (3) judges whether the ablation retreat quantity of the surface of the tested model is larger than a preset boundary movement adjustment threshold value, if so, a motor control signal in a PWM (pulse-width modulation) form is generated, otherwise, a motor control signal in a fixed level form is generated, and the motor control signal is sent to the first servo motor (5-1);
the first servo motor (5-1) drives the moving workbench (6) to move along the moving workbench moving track (7) under the action of a motor control signal, and compensates the ablation retreat amount of the tested model, so that the tested model is kept at the ablation test reference position and is unchanged; synchronously driving the image collector (1) to move along the direction parallel to the moving track (7) of the moving workbench, and ensuring that the relative position of the image collector and the ablation test reference position is kept unchanged;
the image processing computer (2) obtains the boundary information of the tested model in the single frame RGB image, and the specific steps are as follows:
(a) Converting the RGB test image into a gray-scale image;
(b) Filtering all pixel point gray levels to pixel points smaller than a preset gray threshold value, and setting all pixel point gray levels larger than the preset gray threshold value as designated numerical values to obtain a boundary area picture;
(c) Scanning the boundary region picture line by line, scanning all pixel points in each line one by one, continuously taking three pixel points, and marking as a first pixel point, a second pixel point and a third pixel point, if the gray value X1 of the first pixel point, the gray value X2 of the second pixel point and the gray value X3 of the third pixel point simultaneously meet the following two conditions, determining that the second pixel point or the third pixel point is the pixel point of the boundary of the measured model in the boundary region picture, and if not, determining that the first pixel point, the second pixel point and the third pixel point are not the pixel points of the boundary of the measured model in the boundary region picture;
the first condition is as follows:
the ratio of the absolute value of the difference between X1 and X2 to the average of X1 and X2 is less than 10%, i.e. 2 gaming defects X1-X2 |/(X1 + X2) <10%;
the second condition is as follows:
the ratio of the absolute value of the difference between X1 and X3 to the average value of X1 and X3 is greater than 50%, i.e., 2% Y X1-X3 |/(X1 + X3) >50%.
2. The ablation ground simulation test device based on ablation backset compensation is characterized in that the movable workbench (6) and the movable workbench movement track (7) are positioned in a wind tunnel for ablation ground simulation test; the image collector (1), the image processing computer (2), the servo controller (3) and the servo motor (5) are positioned outside the wind tunnel for the ablation ground simulation test; a transparent observation window is arranged on the wind tunnel for the ablation ground simulation test, the image collector (1) records a video of the test process of the tested model through the observation window, and the optical axis of the image collector (1) is parallel to the ablation surface of the tested model (4) and is perpendicular to the axis of the moving workbench moving track (7).
3. The ablation ground simulation test device based on ablation receding amount compensation according to claim 1, wherein the image collector (1) is protected by a filter lens outside a lens to ensure that the CCD of the image collector (1) is not overexposed, and the surrounding is protected by a water circulation cooling system to ensure that the temperature of the outer surface of the image collector (1) is not higher than 45 ℃.
4. The ablation ground simulation test device based on ablation backset compensation according to claim 3, characterized in that the moving track (7) of the moving worktable is made of nickel-based superalloy surface sprayed with yttrium-stabilized zirconia coating material, and the highest surface of the track can withstand the temperature of 1000 ℃.
5. The ablation ground simulation test device based on ablation backset compensation according to claim 3, characterized in that the movable worktable (6) is protected by a high-pressure water circulating cooling system, and the temperature of the device exposed to high-temperature gas is not higher than 150 ℃.
6. The ablation ground simulation test device based on ablation backset compensation is characterized by further comprising a second servo motor (5-2) arranged in the wind tunnel for the ablation ground simulation test;
the servo controller (3) is used for synchronously sending a motor control signal to the first servo motor (5-1) and the second servo motor (5-2);
the first servo motor (5-1) is used for driving the transmission device and the movable workbench (6) to move along the moving track (7) of the movable workbench and compensating ablation backward displacement of the tested model, so that the tested model keeps an ablation test reference position unchanged;
and the second servo motor (5-2) is used for driving the image collector (1), the first servo motor (5-1) and the second servo motor (5-2) to synchronously work, so that the relative position of the image collector and the ablation test reference position is kept unchanged.
7. The ablation ground simulation test device based on ablation backset compensation as claimed in claim 1, wherein the ablation rate of the surface of the tested model to be tested is correlated with the time
The calculation formula of (a) is as follows:
wherein, Δ P = [ Δ P = 1 ,ΔP 2 ,...,ΔP n ]For the difference of the position of each pixel point of the boundary of the tested model, delta P i The position difference of the ith pixel point of the boundary in the tested model image is shown, n is the number of the boundary pixel points in the tested model image, and L is the corresponding physical size of the single pixel point in the tested model image.
8. The ablation ground simulation test device based on ablation retreat amount compensation of claim 1, wherein the calculation formula of the ablation amount R of the surface of the tested model in relation to time is as follows:
wherein S is a sampling period.
9. The ablation ground simulation test device based on ablation retreat amount compensation of claim 1, wherein the threshold is not lower than the minimum displacement of the servo motor capable of controlling the movement of the movable workbench along the movable workbench moving track (7), and the set range is 0.05-1.00 mm.
10. An ablation ground simulation test method based on ablation backward quantity acquisition and compensation is characterized by comprising the following steps:
s1, a tested model (4) is installed on a movable workbench (6), the movable workbench (6) is installed on a movable workbench movement track (7), and the position and the angle of an image collector (1) are adjusted, so that the optical axis of the image collector (1) is parallel to the ablation surface of the tested model (4) and is vertical to the axis of the movable workbench movement track (7);
s2, starting a wind tunnel (8) for an ablation ground simulation test, starting the ablation ground test, simultaneously recording a test process of the tested model (4) by adopting an image collector (1) to obtain continuous video information, and transmitting the video information to an image processing computer (2);
s3, the image processing computer (2) resolves the video information into single-frame RGB images at different moments, analyzes the single-frame RGB images to obtain boundary information of the tested model in each single-frame RGB image, and obtains the surface ablation rate of the tested model related to time based on a pixel calibrated by a standard reference object and a physical length comparison table according to the boundary information of the tested model in the single-frame RGB images at different moments;
s3, the image processing computer (2) sends the ablation backset quantity of the surface of the tested model in the current sampling period, which is obtained by calculating the ablation rate of the surface of the tested model obtained by the latest calculation, to the servo controller (3) according to a preset sampling period, and the step S4 is entered;
s4, the servo controller (3) judges whether the ablation retreating amount of the surface of the tested model is larger than a preset boundary movement adjusting threshold value, if so, the step S5 is executed, otherwise, the step S6 is executed;
s5, the servo controller (3) drives the movable workbench (6) to move along the movable workbench movement track (7) to compensate ablation recession of the tested model;
s6, the image processing computer (2) judges whether the current analysis time reaches the preset test time, and if the current analysis time reaches the preset test time, the test is finished; and if the test time is not reached, skipping to the step S3 to repeatedly execute the step S3 to the step S6.
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